As disclosed, e.g., in U.S. Pat. No. 3,686,025 (Morton) it is known that absorbent flexible substrates can be impregnated with certain surfactants, including some amine oxides, to form laundry dryer sheets that can be used to soften laundry while it is being dried in an automatic dryer.
Because of their ability to act as antistatic agents as well as softening agents, mixed tert-amine oxides, i.e., tert-amine oxides containing at least one long-chain group and at least one short-chain group, are desirable surfactants to use in the preparation of dryer sheets. However, as disclosed in European Patent Application 0307184 (Bauer et al.), such oxides have typically had to be prepared as dilute aqueous solutions in order to avoid gelation problems; and it has been found that the use of such dilute solutions necessitates a drying step in the preparation of laundry dryer sheets and reduces the amount of surfactant that can be incorporated into the sheets.
Copending application Ser. No. 415,910 (Smith et al.), filed Oct. 2, 1989 now abandoned, discloses novel solid non-hygroscopic mixed tert-amine oxide dihydrates and teaches that they may be used as fabric softeners in dry solid laundry detergent compositions. Copending application Ser. No. 591,425) (Borland et al.), filed Oct. 1, 1990, expands upon the teachings of Smith et al. to include mixtures of the dihydrates with monohydrate and anhydrous amine oxide molecules.